This invention relates to the preparation and use of ionic liquids as a superb microwave energy absorbable solvent in microwave-assisted chemical transformations, in particular organic synthesis. The advantages of using low temperature ionic liquids as solvents in microwave-assisted organic synthesis are described.
In the pharmaceutical industry, the need for an increased number of compounds for high-throughput screening puts pressure on the chemist to decrease the time for compound preparation. Microwave-assisted organic synthesis may offer an interesting solution. Microwave-assisted synthesis in organic solvents may, however, involve the risk of an explosion caused by rapid increase in the pressure of the solvent due to difficulties in controlling the application of energy to a reaction mixture.
It has then been suggested to utilise solvent-free microwave-assisted organic synthesis, in that the use of solvent-free reactions is claimed to be an environmentally friendly way of synthesis. Solvent-free synthesis is also considered a safe way of performing organic syntheses at least with respect to increased pressure from the solvent.
However, the environmentally important aspect of solvent-free synthesis is not completely fulfilled since the reagent often has to be dissolved in an organic solvent, e.g. mixed with a solid support material, before evaporation of the solvent before treatment in the microwave cavity. Consequently, organic solvents are, in reality, still used during the synthesis.
Thus, there is a need for improved techniques within in the field of microwave-assisted synthesis.
Ionic liquids are known in organic synthesis (Chem. Commun. (1998) 1765, J. Am. Chem. Soc. 98 (1976) 5277, and references 1-16 listed infra) but their use has been limited predominantly due to their limited solubility or to room temperature reactions. Thus, there is a need to expand the utility of ionic liquids in organic synthesis.
The preparation of ionic liquids is described in WO 95/21871, WO 96/18459 and U.S. Pat. No. 4,624,755. However, these methods require reactions times of up to a week, are problematic due to solubility issues, or require several hours in electrochemical cells. Thus, there is a need for improved methods within in the field of the preparation of ionic liquids.
The invention relates to a method for performing a microwave-assisted chemical transformation, wherein a ionic liquid is used as solvent. More specifically, the method entails an ionic liquid of the general formula I
The invention relates to a method for performing a microwave-assisted chemical transformation, wherein an ionic liquid is used as solvent. More specifically, the method entails an ionic liquid of the general formula I
A+Bxe2x88x92xe2x80x83xe2x80x83(I) 
wherein A+ is an organic cation and Bxe2x88x92 is anion, such as an inorganic anion, which in neat form at a pressure of 1 atmosphere (101.325 kPa) has a melting point of at the most 100xc2x0 C.
A+Bxe2x88x92xe2x80x83xe2x80x83(I)
wherein A+ is an organic cation and Bxe2x88x92 is anion, such as an inorganic anion, which in neat form at a pressure of 1 atmosphere (101.325 kPa) has a melting point of at the most 100xc2x0 C.
An object of the invention is to provide a method for performing a microwave-assisted chemical transformation, wherein an ionic liquid is used as solvent and said ionic liquid is prepared by a microwave-assisted transformation.
Furthermore, the invention relates to a method of preparing ionic liquid by a microwave-assisted transformation.
A further object of the invention is to provide a method of performing a microwave-assisted preparation of an ionic liquid followed by performing a microwave-assisted chemical transformation in one pot wherein said ionic liquid is used as solvent, such as sole solvent, predominant solvent, co-solvent, or additive to an organic solvent in said microwave-assisted chemical transformation.